mm, security: Add lsm hook for set_mempolicy(2)

In container environment, we don't want users to bind their memory to a
specific numa node, while we want to unit control memory resource with
kubelet. Therefore, add a new lsm hook for set_mempolicy(2), then we can
enforce fine-grained control over memory policy adjustment by the tasks in
a container.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>

include/linux/lsm_hook_defs.h

@@ -423,3 +423,5 @@ LSM_HOOK(int, 0, uring_cmd, struct io_uring_cmd *ioucmd)
 LSM_HOOK(int, 0, mbind, unsigned long start, unsigned long len,
 	 unsigned long mode, const unsigned long __user *nmask,
 	 unsigned long maxnode, unsigned int flags)
+LSM_HOOK(int, 0, set_mempolicy, int mode, const unsigned long __user *nmask,
+	 unsigned long maxnode)

include/linux/security.h

@@ -487,6 +487,8 @@ int security_locked_down(enum lockdown_reason what);
 int security_mbind(unsigned long start, unsigned long len,
 		   unsigned long mode, const unsigned long __user *nmask,
 		   unsigned long maxnode, unsigned int flags);
+int security_set_mempolicy(int mode, const unsigned long __user *nmask,
+			   unsigned long maxnode);
 #else /* CONFIG_SECURITY */
 
 static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
@@ -1405,6 +1407,12 @@ static inline int security_mbind(unsigned long start, unsigned long len,
 {
 	return 0;
 }
+
+static inline int security_set_mempolicy(int mode, const unsigned long __user *nmask,
+					 unsigned long maxnode)
+{
+	return 0;
+}
 #endif	/* CONFIG_SECURITY */
 
 #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)

mm/mempolicy.c

@@ -1581,6 +1581,10 @@ static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
 	if (err)
 		return err;
 
+	err = security_set_mempolicy(mode, nmask, maxnode);
+	if (err)
+		return err;
+
 	return do_set_mempolicy(lmode, mode_flags, &nodes);
 }
 

security/security.c

@@ -5344,3 +5344,8 @@ int security_mbind(unsigned long start, unsigned long len,
 {
 	return call_int_hook(mbind, 0, start, len, mode, nmask, maxnode, flags);
 }
+
+int security_set_mempolicy(int mode, const unsigned long __user *nmask, unsigned long maxnode)
+{
+	return call_int_hook(set_mempolicy, 0, mode, nmask, maxnode);
+}